Mutations in the protoporphyrinogen oxidase gene in patients with variegate porphyria

Variegate porphyria (VP) is an acute hepatic porphyria with autosomal dominant inheritance due to a partial deficiency of protoporphyrinogen oxidase (PPOX) activity. The molecular defect responsible for VP was investigated by sequencing PPOX gene coding sequence from four patients in three unrelated VP families of French Caucasian origin. In a first patient, a point insertion of a G at position 1022 of the cDNA, produced a frameshift resulting in a premature stop codon. In three other patients from two unrelated families we found a missense point mutation leading to glycine to arginine substitution (G232R) in exon 7. This Gly232 appears to be a strictly conserved residue through evolution. In one VP family, we observed the cosegregation of the G232R missense mutation and the deficient PPOX activity. The mutations reported here are the first to be described in patients with VP and support the conclusion that PPOX gene defects are disease causing mutations in human variegate porphyria.

Modulation of the phenotype in dominant erythropoietic protoporphyria by a low expression of the normal ferrochelatase allele

Erythropoietic protoporphyria (EPP) is a monogenic inherited disorder of the heme biosynthetic pathway due to ferrochelatase (FC) deficiency. EPP is generally considered to be transmitted as an autosomal dominant disease with incomplete penetrance, although autosomal recessive inheritance has been documented at the enzymatic and molecular level in some families. In the dominant form of EPP, statistical analysis of FC activities documented a significantly lower mean value in patients than in asymptomatic carriers, suggesting a more complex mode of inheritance. To account for these findings, we tested a multiallelic inheritance model in one EPP family in which the enzymatic data were compatible with this hypothesis. In this EPP family, the specific FC gene mutation was an exon 10 skipping (delta Ex10), resulting from a G deletion within the exon 10 consensus splice donor site. The segregation of all FC alleles within the family was followed using the delta Ex10 mutation and a new intragenic dimorphism (1520 C/T). mRNAs transcribed from each FC allele were then subjected to relative quantification by a primer extension assay and to absolute quantification by a ribonuclease protection assay. The data support the hypothesis that in this family the EPP phenotype results from the coinheritance of a low output normal FC allele and a mutant delta Ex10 allele.

Detection by PCR of Toxoplasma gondii in blood in the diagnosis of cerebral toxoplasmosis in patients with AIDS

The polymerase chain reaction (PCR) for amplification of Toxoplasma gondii DNA was performed prospectively in the blood of 19 patients with AIDS and cerebral toxoplasmosis. The B1 gene and TGR1E sequence were used as targets and results were confirmed by hybridisation. Controls consisted of 24 HIV infected patients with tissue culture proven T gondii parasitaemia and 57 HIV infected patients without toxoplasmosis. PCR was positive with both targets in 20 of 24 samples (84%) from patients with parasitaemia. Three of 57 samples (5%) from patients without toxoplasmosis were PCR positive with either target, but none was positive with both targets. Only three of the 19 patients (16%) with cerebral toxoplasmosis had a positive PCR with both targets before the start of specific treatment. PCR performed in blood is of little diagnostic value in cases of cerebral toxoplasmosis but could be useful in patients with disseminated infection.

Increased delta aminolevulinic acid and decreased pineal melatonin production. A common event in acute porphyria studies in the rat

Tryptophan (TRP) is the precursor of melatonin, the primary secretory product of the pineal gland. Hepatic heme deficiency decreases the activity of liver tryptophan pyrrolase, leading to increased plasma TRP and serotonin. As a paradox, patients with attacks of acute intermittent porphyria (AIP), exhibit low nocturnal plasma melatonin levels. This study using a rat experimental model was designed to produce a pattern of TRP and melatonin production similar to that in AIP patients. Pineal melatonin production was measured in response to: (a) a heme synthesis inhibitor, succinylacetone, (b) a heme precursor, delta-aminolevulinic acid (Ala), (c) a structural analogue of Ala, gamma-aminobutyric acid. Studies were performed in intact rats, perifused pineal glands, and pinealocyte cultures. Ala, succinylacetone, and gamma-aminobutyric acid significantly decreased plasma melatonin levels independently of blood TRP concentration. In the pineal gland, the key enzyme activities of melatonin synthesis were unchanged for hydroxyindole-O-methyltransferase and decreased for N-acetyltransferase. Our results strongly suggest that Ala overproduced by the liver acts by mimicking the effect of gamma-aminobutyric acid on pineal melatonin in AIP. They also support the view that Ala acts as a toxic element in the pathophysiology of AIP.

Variegate porphyria: diagnostic value of fluorometric scanning of plasma porphyrins

Variegate porphyria (VP) is a dominantly inherited acute hepatic porphyria characterized by a 50% decrease in activity of protoporphyrinogen oxidase (PO) which catalyses the last step of heme biosynthesis. In VP families, most of the gene carriers are asymptomatic but at risk of developing acute attacks if subjected to precipitating factors. Recognition of the carrier status is the first step of an efficient preventive care. This could be achieved by measurement of PO activity which is a sensitive and specific but tedious method. A specific plasma fluorometric emission at 626 nm has been shown in VP patients. Here we show that this simple and inexpensive method is specific but poorly sensitive, especially in detection of asymptomatic carriers. We conclude that this procedure should not replace PO activity measurement in VP family studies.

Porphobilinogen deaminase gene structure and molecular defects

Porphobilinogen deaminase (PBGD) is the third enzyme of the heme biosynthetic pathway. The half-normal activity of human PBGD causes acute intermittent porphyria (AIP), an autosomal dominant inherited disease. Two PBGD isoforms, one ubiquitous and one erythroid specific, are encoded by a single gene localized to chromosomal region 11q24.1-11q24.2. The 10-kb PBGD gene comprises 15 exons and two distinct promoters initiate the ubiquitous and the erythroid transcripts by alternative splicing. In AIP, diagnosis of asymptomatic heterozygotes is crucial to prevent occurrence of life-threatening acute attacks by avoiding known precipitating factors. Difficulties with the biochemical diagnosis could be overcome by the ability to identify the PBGD gene defects in AIP patients. Mutational analysis of the PBGD gene or the use of intragenic polymorphisms offer accurate identification of the gene carriers. To date, 58 mutations and 10 polymorphisms have been reported at the PBGD locus. The great heterogeneity of the mutations in AIP patients requires appropriate screening and diagnostic strategies to identify gene defects in AIP families.

A molecular defect in coproporphyrinogen oxidase gene causing harderoporphyria, a variant form of hereditary coproporphyria

Hereditary coproporphyria (HC) is an acute hepatic porphyria with autosomal dominant inheritance caused by a deficient activity of coproporphyrinogen IX oxidase (CPX). We previously described harderoporphyria, a homozygous variant form of coproporphyria in three siblings, characterized by a massive excretion of harderoporphyrin and a marked decrease of coproporphyrinogen IX oxidase activity. In this kindred, the transmission of the disease was autosomal recessive. In the present study, sequencing of cDNA and genomic DNA from these patients revealed a point mutation resulting in a lysine to glutamic acid substitution (K304E) in exon 6 of the gene and the absence of the normal allele, suggesting a homozygous state for the mutation. Expression studies of normal and mutated cDNAs in E. coli demonstrated that this amino acid substitution was responsible for the important decrease in the enzyme activity and for the accumulation of harderoporphyrin. The Michaelis constant of the mutated enzyme was 10-fold higher than normal suggesting that the lysine at position 304 is important for binding the substrate: a slightly increased sensitivity to thermal denaturation was also observed.

Detection of eleven mutations causing acute intermittent porphyria using denaturing gradient gel electrophoresis

Acute intermittent porphyria (AIP) is an autosomal dominant disease characterized by mutations of the gene coding for porphobilinogen deaminase (PBGD). Until now, sixteen different mutations have been described. In an effort to investigate further the molecular epidemiology of AIP, we have undertaken a systematic study of different exons of the PBGD gene from a large number of unrelated patients. Here, we have examined seven of the fifteen exons of the gene from 43 unrelated Dutch and French AIP patients using denaturing gradient gel electrophoresis after polymerase chain reaction amplification. Eleven new mutations were found, accounting for the enzymatic defect in about half of the patients. This study further documents the molecular heterogeneity of the mutations responsible for AIP and describes an efficient strategy to detect the mutations in patients with previously unknown abnormalities.

[Hepatic porphyria: diagnostic and therapeutic strategies]

Acute hepatic porphyrias are genetic diseases of heme synthesis with severe prognosis due to strong or acute abdominal pain and neurological complications. Clinical evolution is characterized by acute attacks frequently induced by either forbidden drugs, or infections, alcohol intake or often unknown factors. Modern treatment is perfusion of hematin, which is a stable form of heme. Hematin will induce again delta-aminolévulinic (ALA)-synthase synthesis repression. Its tolerance is perfect whereas clinical and biochemical efficiency is absolute in our experience, if initiated very early. This drug is now considered as the treatment of acute intermittent porphyria crises.

Ferrochelatase structural mutant (Fechm1Pas) in the house mouse

The molecular basis of an inherited defect of ferrochelatase in mouse (Fechm1Pas/Fechm1Pas, described by Tutois et al., 1991, J. Clin. Invest. 88:1730-1736) was investigated. cDNA clones encoding ferrochelatase, isolated by amplification of the mRNA from the liver of a mutant mouse using the polymerase chain reaction, were sequenced by the dideoxynucleotide chain-termination method. All the clones carried a T to A transversion at nucleotide 293, leading to a methionine to lysine substitution at position 98 in the protein (mutation M98K). Hybridization with allele-specific oligonucleotides (ASOs) confirmed the mutation at the cDNA and genomic levels. Finally, expression of the mutant ferrochelatase protein in E. coli demonstrated a marked deficiency in activity in agreement with the activity of the deficient enzyme in vivo. This Fechm1Pas/Fechm1Pas mutant mouse represents a useful model for studying the pathophysiological feature of the human disease and the first accessible model for gene therapy in the field of porphyrias.

High prevalence of a point mutation in the porphobilinogen deaminase gene in Dutch patients with acute intermittent porphyria

Acute intermittent porphyria (AIP) is an autosomal dominant disease characterized by a deficiency of porphobilinogen deaminase (PBGD). Up to now 14 different mutations have been described. In an effort to investigate the molecular epidemiology of AIP we have undertaken a systematic study of different exons of the PBGD gene from a large number of unrelated patients. Here, exon 8 from 82 unrelated Dutch and French AIP patients was examined using single strand confirmation polymorphism analysis (SSCP) after polymerase chain reaction (PCR) amplification. A single base mutation, C to T, at position 346 of the sequence coding for PBGD was observed in 15 Dutch families but in only 1 French family. A simple PCR assay is described to facilitate the diagnosis of this common mutation at the DNA level.

[Acute attacks of hepatic porphyria: specific treatment with heme arginate]

Severe hepatic porphyrias (acute intermittent porphyria, variegate porphyria and hereditary coproporphyria) are hereditary diseases. Each type of porphyria is the result of a specific decrease in the activity of one of the enzymes of heme biosynthesis. Acute attacks are very serious: the abdominal pains are severe and the neurological manifestations can lead to death or incomplete recovery with irreversible sequelae (usually paralysis). Since 1985, the prognosis of acute attacks has been greatly improved by the introduction of heme-arginate. The 69 acute attacks (30 patients, 4 men and 26 women) that we treated with heme-arginate between 1988 and 1991 are described in this report. All patients were infused with 250 mg/d of heme-arginate for 4 days: the mean duration of abdominal pain was 2.5 days (SD 0.72). For 95 p. 100 of the attacks, the total hospitalization time was 5 days or less; side effects were very minor. In every case, a favorable response was dependent upon the early initiation of heme therapy.

Decreased nocturnal plasma melatonin levels in patients with recurrent acute intermittent porphyria attacks

Acute intermittent porphyria (AIP) is a hereditary disease characterized biochemically by a defect in the heme pathway enzyme porphobilinogen deaminase. There is wide variability in the neurologic clinical expression of AIP, and the disorder remains latent in most gene carriers. The natural history of the disease and results in a porphyric rat model suggest a significant relationship between tryptophan metabolites and clinical expression of the disease. In the present study, we examined urine and blood tryptophan metabolite levels in AIP women before, during and after acute attacks and treatment by heme arginate. Heme arginate treatment promptly decreased total tryptophan levels (from 69 +/- 9, to 44 +/- 5, mean +/- SEM, mumole/l, p < 0.001), serotonin blood levels (from 629 +/- 103, to 356 +/- 80, nmole/l, p < 0.01) and the urinary excretion of 5-HIAA (from 3.9 +/- 0.6, to 2.2 +/- 0.4, mumole/mmole creatinine, p < 0.01). The plasma level of melatonin was found much lower than the normal control level at night (86.2 +/- 70.3, vs the normal range, 409 +/- 78.9, pmole/l +/- SEM) and day time (38.8 +/- 22.0, vs 75 +/- 13.7). Heme arginate treatment did not influence melatonin levels. Our results support the involvement of abnormal tryptophan metabolism in the pathophysiology of AIP acute attacks. Low melatonin plasma levels in porphyric women suggest that the defect of the pineal hormone may be responsible for the recurrent aspect of porphyric attacks. A desynchronization of biological rhythms in AIP patients may increase the inducibility of hepatic ALA synthase to environmental risk factors and, specially, to sex steroid hormones.

Denaturing gradient gel electrophoresis for rapid detection of latent carriers of a subtype of acute intermittent porphyria with normal erythrocyte porphobilinogen deaminase activity

Acute intermittent porphyria is an autosomal dominant disorder defined by a partial deficiency of porphobilinogen deaminase (EC 4.3.1.8). Clinical manifestations of the disease are characterized by acute attacks of neurological dysfunction often linked to environmental factors. Early diagnosis of gene carriers is important in the prevention of attacks and is usually achieved by determining the porphobilinogen deaminase activity in erythrocytes. However, in a subtype of acute intermittent porphyria, the enzymatic defect is restricted to nonerythropoietic cells. Different mutations have already been described that account for this phenotype in two unrelated families. We previously detected asymptomatic carriers by using mutation-specific probes after in vitro amplification of the target DNA sequence. In this study, we investigated the DNA of eight unrelated subjects with the same subtype of acute intermittent porphyria by using the polymerase chain reaction, with subsequent analysis of the amplified products by denaturing gradient gel electrophoresis. Five of these patients shared the same single-base change. This technique was quite simple and efficient for detecting asymptomatic carriers. Importantly, it is potentially useful for studying families with the same phenotypic subtype of the disease and possibly different mutations in the same DNA region.

Heterogeneity of mutations in the uroporphyrinogen III synthase gene in congenital erythropoietic porphyria

Congenital erythropoietic porphyria (CEP) or Günther's disease is an inborn error of heme biosynthesis transmitted as an autosomal recessive trait and characterized by a profound deficiency of uroporphyrinogen III synthase (UROIIIS) activity. We have previously described two missense mutations in the UROIIIS gene, confirming that the primary defect responsible for CEP is a structural alteration of this gene. We have extended our work to 5 additional unrelated families. Two new point mutations, a deletion and an insertion have been found in the messenger RNA. Our study shows that a molecular heterogeneity of the mutations exists in Günther's disease. One mutation (C73R), however, appears to be more frequent than the others. Finally, the different normal and mutated proteins have been expressed in Escherichia coli to determine the consequence of the mutations on the enzyme activity.

Denaturing Gradient Gel Electrophoresis for Rapid Detection of Latent Carriers of a Subtype of Acute Intermittent Porphyria with Normal Erythrocyte Porphobilinogen Deaminase Activity

Acute intermittent porphyria is an autosomal dominant disorder defined by a partial deficiency of porphobilinogen deaminase (EC 4.3.1.8). Clinical manifestations of the disease are characterized by acute attacks of neurological dysfunction often linked to environmental factors. Early diagnosis of gene carriers is important in the prevention of attacks and is usually achieved by determining the porphobilinogen deaminase activity in erythrocytes. However, in a subtype of acute intermittent porphyria, the enzymatic defect is restricted to nonerythropoietic cells. Different mutations have already been described that account for this phenotype in two unrelated families. We previously detected asymptomatic carriers by using mutation-specific probes after in vitro amplification of the target DNA sequence. In this study, we investigated the DNA of eight unrelated subjects with the same subtype of acute intermittent porphyria by using the polymerase chain reaction, with subsequent analysis of the amplified products by denaturing gradient gel electrophoresis. Five of these patients shared the same single-base change. This technique was quite simple and efficient for detecting asymptomatic carriers. Importantly, it is potentially useful for studying families with the same phenotypic subtype of the disease and possibly different mutations in the same DNA region.

Human erythropoietic protoporphyria: two point mutations in the ferrochelatase gene

The molecular basis of the ferrochelatase defect responsible for human Erythropoietic Protoporphyria (EPP), a usually autosomal dominant disease, was investigated in a family with an apparently homozygous patient. Two mutations of the ferrochelatase gene were identified by sequencing the proband's cDNA after in vitro amplification of the mRNA and subcloning of the amplified products. One mutation results from a G to T transition at nucleotide 163 which produces a glycine to cysteine substitution at amino-acid residue 55 (G-55-C). The other one was a G to A change at nucleotide 801, leading to a methionine to isoleucine substitution at amino-acid residue 267 (M-267-I). This EPP patient was then double heterozygous and as expected each of his parents carried one of the mutations. A second similar EPP patient was screened for these mutations with negative results, showing a genetic heterogeneity in EPP.

Erythropoietic protoporphyria in the house mouse. A recessive inherited ferrochelatase deficiency with anemia, photosensitivity, and liver disease

A viable autosomal recessive mutation (named fch, or ferrochelatase deficiency) causing jaundice and anemia in mice arose in a mutagenesis experiment using ethylnitrosourea. Homozygotes (fch/fch) display a hemolytic anemia, photosensitivity, cholestasis, and severe hepatic dysfunction. Protoporphyrin is found at high concentration in erythrocytes, serum, and liver. Ferrochelatase activity in various tissues is 2.7-6.3% of normal. Heterozygotes (+/fch) are not anemic and have normal liver function; they are not sensitive to light exposure; ferrochelatase activity is 45-65% of normal. Southern blot analysis using a ferrochelatase cDNA probe reveals no gross deletion of the ferrochelatase gene. This is the first spontaneous form of erythropoietic protoporphyria in the house mouse. Despite the presence in the mouse of clinical and biochemical features infrequent in the human, this mutation may represent a model for the human disease, especially in its severe form.

Molecular heterogeneity of acute intermittent porphyria: identification of four additional mutations resulting in the CRIM-negative subtype of the disease

Four mutations of the porphobilinogen (PBG) deaminase gene that result in cross-reacting immunological material (CRIM)-negative forms of acute intermittent porphyria (AIP) have been identified by in vitro amplification of cDNA from patients and by cloning of the amplified products in a bacterial expression vector. One mutation is a single base deletion which causes a frameshift and which is expected to result in the synthesis of a truncated protein. Two other mutations consist of single base substitutions and lead to amino acid changes. The fourth mutation is a single base substitution producing an aberrant splicing and resulting in an mRNA which would encode a protein missing three amino acids. DNAs from 16 unrelated CRIM-negative AIP patients were screened for the presence of these four mutations, by hybridization with oligonucleotides specific for each of the mutations, but none of the four mutations was identified in additional patients. The results indicate that mutations responsible for CRIM-negative AIP are highly heterogenous.

Two different point G to A mutations in exon 10 of the porphobilinogen deaminase gene are responsible for acute intermittent porphyria

Two mutations of the porphobilinogen (PBG) deaminase gene resulting in cross-reacting immunological material (CRIM) positive forms of acute intermittent porphyria (AIP) have been identified by in vitro amplification of cDNA and cloning of the amplified products in a bacterial expression vector. Both mutations resulted from G to A transitions in exon 10 of the gene and produced arginine to glutamine substitutions in the abnormal protein. Expression of mutant cDNA in Escherichia coli reveals that one but not the other of these amino acid changes results in a striking decrease of the optimal pH of the mutated enzyme. One or the other of these two mutations accounted for the defect causing AIP in six unrelated patients among the eight patients evaluated with the CRIM positive subtype of this disorder.

Point mutations in the uroporphyrinogen III synthase gene in congenital erythropoietic porphyria (Günther's disease)

Congenital erythropoietic porphyria (Günther's disease) is a rare disorder of heme biosynthesis inherited in an autosomal recessive fashion. The molecular abnormality responsible for the characteristic defect in uroporphyrinogen III synthase activity was investigated in two patients. For the first patient, complementary DNA was specifically amplified using the polymerase chain reaction and subsequently cloned and sequenced. Data obtained revealed the coexistence of two distinct point mutations: a T to C change in codon 73 (arginine in place of a cysteine) and a C to T change in codon 53 (leucine in place of a proline). The second case was studied by hybridization with allele specific oligonucleotides and was found to be homozygous for the same mutation in codon 53. These are the first mutations to be recognized in the uroporphyrinogen III synthase gene from congenital erythropoietic porphyria patients.

A retrospective study of a patient with homozygous form of acute intermittent porphyria

In 1964 a child with an exceptional form of porphyria was described; she excreted persistently excessive amounts of delta-aminolaevulinic acid, porphobilinogen and uroporphyrin in her urine from early childhood. The biochemical profile resembled that of acute intermittent porphyria (AIP). The child died at the age of 8 years. Reinvestigation of some urine samples by HPLC revealed differences in comparison with urines of other patients with AIP. The clinical picture characterized by porencephaly and severe retardation in development was completely different from that of AIP. Her mother suffered from AIP but the father never had attacks. Investigations on blood and urine samples of the father showed that he also was affected. Due to the early onset in the index patient, its persistent character, and the fact that both parents are affected we postulate retrospectively to have diagnosed a case of homozygous or a double heterozygous AIP, hitherto undescribed.